Relationship between average burnup (В, MW·day/kgU), enrichment (х, %) and refueling multiplicity (n≥1) for uranium fuel for different thermal neutron reactors. Source: plotted by authors based on experimental and calculated data in OECD/NEA 2006, ORNL 2012, NF-T-3.8 2011, Jatuff 2016, Semchenkov et al. 2011, Nuclear Fuels 2009, Xu 2003, RBMK Channel Nuclear Reactor 2006, Lee et al. 2007. The straight lines are the calculation using formula (8) for different n=1−8. The polygons reflect the boundaries of the grid diagrams obtained as the result of neutronic calculations in Jatuff 2016, Semchenkov et al. 2011, Nuclear Fuels 2009, Xu 2003 for PWR and VVER reactors.